This invention relates to a thermal energy storage apparatus and particularly to an apparatus for storing thermal energy in the form of heat of fusion for extended period of storage.
Energy storing systems have been suggested to permit storage of the thermal energy from a suitable source during low peak usage periods or when such energy is available for subsequent use as necessary. The rather serious questions which have recently developed with respect to the availability and cost of natural resources in the world have increased the interest in development of heat storage systems, particularly those which are useful to store solar energy and the like.
Although many different thermal storage energy systems have been suggested, basically three different storage types are available and can be generally classified as (1) liquid storage, (2) solid or packed bed storage, and (3) phase change storage.
Liquid storage systems widely employ water as the thermal energy storage medium. The thermal energy is stored by heating of the liquid and storing it within a suitable thermally insulated container. The solid or packed storage system generally operates in a similar manner but employs rocks, pebbles and the like which are heated to store the energy. Phase change energy storage employs materials which are changed in phase, generally to a gaseous state from a liquid state or to a liquid state from a solid state. For example, certain systems of the first type employ conversion of water to steam. Systems of the second type employ conversion of a sodium salt to a liquid in accordance with the well-known equation: Na.sub.2 SO.sub.4.10H.sub.2 O.fwdarw.Na.sub.2 SO.sub.4 +10H.sub.2 O. Although such devices have been suggested, the various designs generally have certain inefficiencies and complexities connected with the storage and recovery of energy.